1. Field of the Invention
The instant invention is a method for the control of undesirable plants by use of plant pathogens.
2. Description of the Prior Art
The merits for using plant pathogens to control weeds in annual crops have been discussed previously for two Colletotrichum spp. (Daniel, et al. U.S. Pat. No. 3,849,104 and Templeton, U.S. Pat. No. 3,999,973). The anthracnose fungus Colletotrichum gloeosporioides has been used to control the weed northern jointvetch, and another strain of this fungus has been used to control winged waterprimrose. Colletotrichum malvarum has been used to control prickly sida. These three pathogens have been combined to control all three target weeds at once. In other work the fungus Alternaria macrospora has been used to control spurred anoda. Alternaria macrospora, Weed Science, L. Walker 1981, Vol. 29, pp 505-507.
A major constraint to commercial development of a plant pathogen as a biological herbicide is selectivity. A pathogen that controls only one weed species in one crop does not have the same market potential as a pathogen that controls several important weeds in several crops. In all prior work, no one pathogen has been found that would control two or more important weed species.
Prickly sida is an annual broadleaf herb, that is naturalized from South America. This weed is a pest in soybeans and cotton. Yield reductions occur at low weed densities. Seedlings emerge throughout the growing season, and multiple chemical herbicide applications are necessary to control the weed. This species is a member of the Malvaceae, and is closely related to cotton. The herbicides norflurazon and bentazon are commonly used to control prickly sida in cotton and soybeans, respectively. One plant pahthogen (Colletotrichum malvarum) has been tested experimentally for the control of prickly sida, U.S. Pat. No. 3,999,973.
Velvetleaf, a native of Asia, is also closely related to cotton. This species, a broadleaf annual, is a serious weed problem in soybeans, corn, and cotton. Significant crop yield losses occur at low weed densities. Present control methods are limited to cultivation and chemical herbicides. Norflurazon, bentazon, and 2,4-D are commonly used in cotton, soybeans, and corn, respectively.
Spurred anoda is an annual broadleaf species that is native to South America and the Southwestern United States. This weed which is closely related to cotton is a serious pest in cotton and is increasing in importance in soybeans and several other agronomic crops in the Southern United States. Spurred anoda is a strong competitor with crop plants, and even low weed densities, this weed produces significant crop yield losses. Even partial control can be difficult and expensive. Present control methods for spurred anoda are limited to cultivation, and to multiple applications of chemical herbicides. Norflurazon is used for control in cotton, and bentazon is used to control this weed in soybeans. Plants larger than the fifth leaf stage are difficult to control with any of the commonly used herbicides. The fungus Alternaria macrospora has been used experimentally to control spurred anoda. Alternaria macrospora, Weed Science, L. Walker, 1981, Vol. 29, pp. 505-507.